Analysis of the improvement effect of expansive soil through the soil-water characteristic curve

This study aims to establish the relationship between the theory of unsaturated soil and the corresponding engineering problem by using the soil-water characteristic curve to determine the improvement effect of expansive soil. The contents of two improvers, i. e. , lime and fly ash, were added into Baise expansive soil for free expansion ratio testing. Based on the optimum moisture contents determined by using the modified Proctor compaction method, testing specimens of each improved soil sample were obtained. By dewetting the soil-water characteristic curve testing in the range of 5 kPa to 1 000 kPa by using a pressure plate apparatus, the expansion properties and soil-water characteristic curves of the improved expansive soils were determined. The effect of different improvers and mixing contents on the soil-water characteristic curves, which were fitted by the variance gamma model, was analyzed based on the theory of unsaturated soil and on the national determination criterion for expansive soils. Saturated gravity water content, air entry value, residual water content, and curve slope were found to have potential for use in evaluating the chemical improvement effect on expansive soils. Further analysis shows that the improvement effect can be determined if three of the four indexes of expansive soil meet the requirements. However, saturated gravity water content is indispensable, but any two of the remaining three indexes can be considered.